The vertebral disc is a collagenous spacer positioned between the vertebral bones of the spinal column. The disc generically consists of a tough fibrillar outer annulus (annulus fibrosus) and a highly hydrated gelatinous core (nucleus pulposus). The vertebral disc serves as a shock absorber to dissipate the energy of impact loading on the back, as well as a joint, allowing flexion and extension of the human torso.
Degeneration of vertebral disc function in the lumbar portion of the spine is the leading cause of debilitating low back pain in adults over the age of 35. Degenerative disc disease (DDD) is characterized by a gradual collapse of the vertebral disc due to dehydration of the nucleus pulposus, or by a bulging of the annulus fibrosus. DDD may also precipitate the formation of fissures within the annulus that allows extrusion of the disc nucleus (disc herniation) resulting in a sudden collapse in the disc height and the potential for nerve root and/or spinal cord compression. Disc herniation may also result due to trauma related over compression of the spine, such as a heavy sitting fall.
Chronic diffuse low back pain results from irritation of pain receptors in the outer third of the disc annulus and surrounding soft tissues as the disc collapses. Radicular pain results from direct compression of the affected nerve root by extruded or bulging disc tissue. Aggressive and extensive physical therapy and drug treatments are the first line treatments for debilitating back pain. In the absence of acceptable pain resolution, surgical intervention is indicated.
The traditional surgical procedures for treatment of intractable low back pain due to DDD call for either fusion of the vertebral bodies above and below the affected disc, or removal of the nuclear material thorough open surgical, micro-surgical or endoscopic procedures. Recently, novel procedures involving thermal shrinkage of the collagenous lamina with an electrothermal catheter or laser device have been applied. The removal of the nucleus leaves a void within the disc, and eliminates the viscoelastic fluid that acts as a shock absorber. This void and absence of the viscoelastic fluid creates an opportunity for the lamina to collapse inward and allows the disc space to collapse further. The collapse of the disc space can lead to loss of motion and morbidity, as during the collapse of the disc space the nerves radiating from the spinal column may be pinched.
Many surgical techniques and specialized devices have been generated to combat the problem of progressive disc collapse resulting from disc denucleation. Harvested autologous bone has been placed within the denucleated disc space to afford a bony bridge or fusion between the two vertebral bodies. Pedicle screws and other spinal instruments, such as rods and plates, are mechanically affixed to the vertebral bodies, stabilizing the vertebra and preventing further collapse. The problem with these, and other fusion techniques, is the prevention of motion at the level of repair, and resultant transfer of stresses to the levels above and below. These additional loading stresses inevitably result in the degeneration of these disc levels as well.
The patent literature discloses several apparati for the replacement of an entire disc (i.e., prosthetic vertebral disc), whereby the damaged disc is removed and a device is anchored to the vertebral bone below and above the damaged disc. The ultimate goal of such a design concept is to maintain or regain the mobility of the native vertebra-disc-vertebra motion segment. Varying degrees of mobility have been claimed for different types of mechanical disc replacements. The following is a non-exhaustive list of such U.S. Patent disclosures;1 U.S. Pat. No. 4,309,777 to Patil; U.S. Pat. No. 5,865,845 to Thalgott; U.S. Pat. No. 5,827,328 to Buttermann; U.S. Pat. No. 5,865,846 to Bryan et al; U.S. Pat. No. 4,759,766 to Buettner-Jantz et al.; U.S. Pat. No. 5,071,437 to Steffe; U.S. Pat. No. 4,911,718 to Lee at al.; and U.S. Pat. No. 4,714,469 to Kenna. The utility of these prior design proposals has been principally limited by an inability to adequately anchor the flexible prosthetic disc to the bony vertebra. 1 The entire disclosure of each U.S. Patent cited hereinafter is hereby expressly incorporated hereinto by reference.
An alternate approach to the repair of damaged or diseased vertebral discs is to physically prevent disc collapse through the insertion of a rigid body into the disc space. The insertion of tubular or other hollow devices, that may, in addition, contain openings through their walls to allow bone growth through the device, enable the motion segment to be fused with the vertebral spacing maintained. These open or tubular devices may be constructed of metallic alloys traditional to implantable medical devices (e.g., stainless steel, titanium and titanium alloys), carbon fiber reinforced engineering thermoplastics (e.g., polyetheretherketones), or machined human cortical bone. These devices have been disclosed, for example, in U.S. Pat. No. 4,961,740 to Ray et al; U.S. Pat. No. 5,015,247 to Michelson; U.S. Pat. No. 5,766,253 to Brosnahan; U.S. Pat. No. 5,425,772 to Brantigan; and U.S. Pat. No. 5,814,084 to Grivas et al. While these devices may retain the proper spacing between the vertebra (i.e., the disc height), they are disadvantageous since, as the two vertebrae are fused, motion across the vertebra-disc-vertebra element is eliminated.
Another general technique for the preservation of vertebral body separation is to replace the removed disc nuclear tissue with non-fusing, non-rigid materials. One prior proposal suggests using a bladder that can be filled with liquid to restore disc height (see, U.S. Pat. No. 3,875,595 to Froning). One other prior proposal is disclosed in U.S. Pat. No. 5,534,028 to Bao et al, where a pre-cast pre-shaped hydrogel in placed into the void. Variations on the type of device disclosed in Bao et al '028 are likewise disclosed in U.S. Pat. Nos. 5,976,186, 5,192,326, and 5,047,055. Preformed inserts made from a xerogel plastic as a nucleus pulposus replacement have also been disclosed in U.S. Pat. No. 6,264,695. A cylindrical hydrogel pillow that is contained within a non-expanding casing and assorted variations thereof are described in U.S. Pat. Nos. 4,772,287, 4,904,260, 5,674,295, 5,824,093, and 6,022,376. In this regard, the device shown in U.S. Pat. No. 6,022,376 is inserted into tunnels drilled into the disc as a dehydrated hydrogel resin, and is allowed to rehydrate and swell once it is inserted. The swelling holds the device in place while preventing the collapse of the denucleated disc. However, the device is neither chemically nor mechanically fixated in place.
It has also been disclosed in U.S. Pat. Nos. 6,183,581, 6,206,921 and 6,264,659, that molten gutta percha and its compounds may be used as possible replacements of nucleus pulposus.
Broadly, the present invention relates to bioprosthetic devices comprised of an exterior biological tissue member which at least partly defines a cavity, and a proteinaceous biopolymer which fills the cavity, and intercalates is chemically bound (linked) to the surrounding biological tissue member. In preferred forms, the bioprosthetic device is a bioprosthetic vertebral disc having a fibrillar outer annulus which surrounds and defines an interior cavity and is formed by removal of at least a substantial portion of the natural gelatinous core therefrom. The cavity defined by the fibrillar outer annulus may then be filled with a flowable biopolymeric material which is then allowed to at least partly solidify in situ (e.g., most preferably by in situ cross-linkage reaction) to form a proteinaceous biopolymer within the cavity.
The flowable biopolymeric material is most preferably a liquid mixture liquid mixture comprised of human or animal-derived protein material and a di- or polyaldehyde. When introduced into the cavity of the tissue member, therefore, the liquid mixture may then react to form a cross-linked biopolymer in situ within the cavity thereby forming a bioprosthetic device therein. The liquid mixture may be formed in advance of being introduced into the cavity, or may be formed simultaneously during introduction into the cavity.
These and other aspects and advantages will become more apparent after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.